Re: [PATCH v2 7/7] s390/cio: Remove vfio-ccw checks of command codes

From: Cornelia Huck <cohuck@redhat.com>
To: Eric Farman <farman@linux.ibm.com>
Cc: Farhan Ali <alifm@linux.ibm.com>,
	Halil Pasic <pasic@linux.ibm.com>,
	Pierre Morel <pmorel@linux.ibm.com>,
	linux-s390@vger.kernel.org, kvm@vger.kernel.org
Subject: Re: [PATCH v2 7/7] s390/cio: Remove vfio-ccw checks of command codes
Date: Wed, 15 May 2019 14:43:05 +0200	[thread overview]
Message-ID: <20190515144305.46a2ecb1.cohuck@redhat.com> (raw)
In-Reply-To: <20190514234248.36203-8-farman@linux.ibm.com>

On Wed, 15 May 2019 01:42:48 +0200
Eric Farman <farman@linux.ibm.com> wrote:

> If the CCW being processed is a No-Operation, then by definition no
> data is being transferred.  Let's fold those checks into the normal
> CCW processors, rather than skipping out early.
> 
> Likewise, if the CCW being processed is a "test" (an invented
> definition to simply mean it ends in a zero), let's permit that to go
> through to the hardware.  There's nothing inherently unique about
> those command codes versus one that ends in an eight [1], or any other
> otherwise valid command codes that are undefined for the device type
> in question.

Hm... let's tweak that a bit? It's not that "test" is an invented
category; it's just that this has not been a valid command for
post-s/370 and therefore should not get any special treatment and just
be sent to the hardware?

> 
> [1] POPS states that a x08 is a TIC CCW, and that having any high-order
> bits enabled is invalid for format-1 CCWs.  For format-0 CCWs, the
> high-order bits are ignored.
> 
> Signed-off-by: Eric Farman <farman@linux.ibm.com>
> ---
>  drivers/s390/cio/vfio_ccw_cp.c | 11 +++++------
>  1 file changed, 5 insertions(+), 6 deletions(-)